But previous research has shown this defensive regurgitating ends up harming the insects by slowing down the caterpillars’ growth, reducing their survival rates, and even lowering the number of female eggs, according to the University of Bristol.

Now a new study in Ecology Letters shows that a caterpillar is more likely to vomit alone than when when its hanging out with its peers.

“Caterpillars take account of their group size when ‘deciding’ whether to vomit because they are trying to avoid the cost of vomiting,” study co-author Mike Speed of the U.K.’s University of Liverpool said in a statement.

“In a group, it is quite likely that the predator will taste other individuals as well, each of whom might vomit and cause the predator to give up and leave,” Speed said.

“Also, caterpillars compete with each other for food, and so the bigger the group the more important it is to not vomit.”

By studying P. brassicae‘s vomiting strategy, the scientists hope to crack the defensive secrets of other crop pests, which in turn may inspire better methods for combating pests.

“The obvious pressure on caterpillars to limit the use of their defenses suggests that predators of crop pests have a far greater benefit on crops than simply the number of insects that they eat. Just trying to eat caterpillars reduces the fecundity of such pests and helps out farmers,” said study co-author Andrew Higginson, an ecologist at the University of Bristol.

Wrote Ker Than, “Other mammals are known to use toxins that they don’t produce themselves. For example, a hedgehog species applies a mild toxin from a toad to its fur. … Likewise, some capuchin monkeys rub an extract from millipedes onto their fur to repel insects.”

People have also picked up some hints from their animal brethren: African hunters use the same plant toxin as the crested rat to make elephant-grade poison arrows.

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